1. Field of the Invention
The present invention relates to a solution containing whey protein which undergoes gelation by the addition of salt-derived ions; a gel produced by gelation of the solution; a powder produced by drying the solution; and processed food products in which the solution, gel or powder is used. The technology related to the present invention is applicable in the field of food manufacturing in which the gelation property and water-retention capacity are necessary.
2. Description of the Prior Art
Whey protein is a general term for proteins present in milk which includes lactoalbumin, lactoglobulin and other proteins and is characterized by the fact that it is heat-denatured at a temperature between 72.degree. and 75.degree. C., and that it can coagulate at a higher temperature than this temperature range.
Accordingly, a heating method is well-known in general as a means of gelation of a whey protein solution and essentially no other means are available.
Considerable research has been carried out on the heat-induced gelation of whey protein and heat-coagulated products of whey protein (Journal of Food Science, 53(1), 231-236, 1988; Nihon Shokuhin Kogyo-Gakkai, 32(9), 639-645, 1985). These gelated products and heat-coagulated products are heated in the presence of salts. However, such heat-induced gels have problems in common, viz., their water-retention capacity is reduced over time and their texture is not smooth enough, although these problems are mostly originated from the salt concentration.
In addition, gelation occurs with heat treatment whereby heating has to be carried out under static conditions. On an industrial scale, it is difficult to manufacture a large amount of gel under these static conditions. In other words, in heating a large mass to obtain a large volume of gel, a long period of time is required to attain the temperature for gelation at the center of the mass, which causes overheating around the peripheral part of the mass, resulting in undesirable scorching and pore formation around the edges. Furthermore, because of the heat treatment, the gels are used limitedly only as supplemental materials in food processing.